From the first moment when Silas discovered Eppie on his hearth, and he confused her with his gold, it is clear that Eppie becomes as important (if not more) to Silas as his gold had been. Note how the narrator says when Silas has Eppie on his knee:

Thought and feeling were so confused within him, that if he had tried to give them utterance, he could only have said that the child was come instead of the gold--that the gold had turned into the child.

So, in the mind of Silas at least, Eppie is a gift sent from above as replacement for his lost treasure. However, as Chapter 14 goes on to tell us, there are some significant differences between Eppie and the gold:

The gold had kept his thoughts in an ever-repeated circle, leading to nothing beyond itself; but Eppie was an object compacted of changes and hopes that forced his thoughts onward, and carried them away from their old eager pacing towards the same blank limit--carried them away to the new things that would come with the coming years, when Eppie would have learned to understand how her father Silas cared for her; and made him look for images of that time in the ties and charities that bound together the families of his neighbours. The gold had asked that he should sit weaving longer and longer, deafened and blinded more and more to all things except the monotony of his loom and the repetition of his web; but Eppie called him away from his weaving, and made him think all its pauses a holiday, reawakening his senses with her fresh life, even to the old winter-flies that came crawling forth in the early spring sunshine, and warming him into joy because she had joy.

Thus we can see that whilst in Silas' mind he considers Eppie to be a replacement for the gold, the impact on his own life is incredibly different. Eppie opens him up, "reawakening" him once again to the joy of life and love, rather than being so fixated on greed and the gain of wealth, as he had been before. Therefore Eppie is a much healthier influence on him than his gold had been.